1. Field of the Invention
The present invention relates to a mixer for a multicylinder gas engine having a plurality of intake passages extending to a plurality of cylinders of the engine and a plurality of gaseous fuel nozzles, wherein each nozzle has a nozzle orifice opening in a corresponding intake passage. The intake passages and fuel nozzles are provided in a mixer main body and the fuel nozzles are connected to a gaseous fuel supply device.
2. Related Art
In a conventional mixer for a multicylinder gas engine, a gaseous mixture of a gaseous fuel and air formed in a common intake passage is distributed to a plurality of cylinders of the engine via an intake manifold.
Since the above-described arrangement employs a single common intake passage for a plurality of cylinders, the structural arrangement is simple and can be provided at a low cost. However, the influence of interference between the cylinder intakes makes uniform distribution of the gaseous mixture among the cylinders difficult. In order to avoid the influence of interference between the cylinder intakes, theoretically, each cylinder could be provided with a separate mixer, but in practice, such an arrangement would greatly increase the number of parts, thereby resulting in an undesirable increase in cost.
It is an object of the present invention to overcome the above-described drawbacks of the conventional gas engine mixer.
It is also an object of the present invention to provide a mixer for a multicylinder gas engine that achieves uniform distribution of a gaseous mixture to each cylinder while minimizing any increase in the number of parts, and prevents fluctuations in the fuel concentration of the gaseous mixture due to pulsations in the intake pressure.
According to a preferred embodiment of the present invention, a mixer is provided for a multicylinder gas engine in which a plurality of intake passages extend to a plurality of cylinders of the engine. A plurality of gaseous fuel nozzles, each having a nozzle orifice opening in a corresponding intake passage, are provided in a mixer main body. The plurality of gaseous fuel nozzles are connected to a gaseous fuel supply device. A common surge tank housing the plurality of gaseous fuel nozzles and having a fuel intake pipe opening therein is provided on the mixer main body. The fuel intake pipe extends to the gaseous fuel supply device and intake pressure pulsations that have passed through the gaseous fuel nozzles are attenuated within the surge tank.
Because the plurality of intake passages are separated from each other so as to correspond to the plurality of cylinders of the engine, even if there is a difference in the intake timing of the plurality of cylinders that causes a difference in the timing of an intake negative pressure acting on each of the intake passages, the intake passages are not affected by interference between the cylinder intakes, and equalization of the intake volumes of the cylinders is achieved. Furthermore, since the surge tank is between the plurality of gaseous fuel nozzles, even when an intake pressure pulsation reaches one of the intake passages, the intake pressure pulsation enters the surge tank via the corresponding gaseous fuel nozzle and is attenuated, thereby preventing the intake pressure pulsation from having any influence on another gaseous fuel nozzle. As a result, each of the gaseous fuel nozzles issues a precise amount of gaseous fuel into the corresponding intake passage according to the degree of negative pressure generated in the intake passage. Accordingly, fluctuations in the fuel concentration of the gaseous mixture supplied to each of the cylinders is prevented, thereby stabilizing operation of the engine. Moreover, use of the common surge tank as an intake pressure attenuator reduces the number of parts and keeps any costs to a minimum.
According to a second embodiment of the present invention, the volume of the surge tank is set at 20% or more of the displacement of the engine. Thus, the surge tank reliably attenuates the intake pressure pulsations to ensure stable operation of the engine.
According to a third embodiment of the present invention, the nozzle orifice of each gaseous fuel nozzle is positioned at substantially the center of the corresponding intake passage. Thus, a negative pressure generated by a flow of air passing through each of the intake passages acts effectively on the nozzle orifice of the corresponding gaseous fuel nozzle. The structure of the third embodiment allows a precise amount of gaseous fuel to be issued into the intake passage according to the level of the negative pressure, thus achieving further stabilization of the fuel concentration of the gaseous mixture.
According to a fourth embodiment of the present invention, disposed between each of the plurality of gaseous fuel nozzles and the common fuel intake pipe is a unidirectional valve that allows fuel to flow in only one direction from the latter to the former. Thus, cooperation between the unidirectional valve and the surge tank further enhances the effect of attenuating the intake pressure pulsations.